Influence of fine structures on gyrosynchrotron emission of flare loops modulated by sausage modes

TL;DR

This study models how fine structures in solar flare loops influence gyrosynchrotron emission modulated by sausage modes, revealing that sausage modes remain observable as a QPP mechanism despite fine structures.

Contribution

It provides the first detailed forward modeling of gyrosynchrotron emission considering fine structures and sausage mode modulation in flare loops.

Findings

Low- and high-frequency intensities oscillate in-phase with sausage modes.

Fine structures reduce modulation at low frequencies and certain viewing angles.

High-frequency emissions are minimally affected by fine structures.

Abstract

Sausage modes are one leading mechanism for interpreting short period quasi-periodic pulsations (QPPs) of solar flares. Forward modeling their radio emission is crucial for identifying sausage modes observationally and for understanding their connections with QPPs. Using the numerical output from three-dimensional magnetohydrodynamic (MHD) simulations, we forward model the gyrosynchrotron (GS) emission of flare loops modulated by sausage modes and examine the influence of loop fine structures. The temporal evolution of the emission intensity is analyzed for an oblique line of sight crossing the loop center. We find that the low- and high-frequency intensities oscillate in-phase at the period of sausage modes for models with or without fine structures. For low-frequency emissions where the optically thick regime arises, the modulation magnitude of the intensity is dramatically reduced by the fine structures at some viewing angles. On the contrary, for high-frequency emissions where the optically thin regime holds, the effect of fine structures or viewing angle is marginal. Our results show that the periodic intensity variations of sausage modes are not wiped out by the fine structures, and sausage modes remains a promising candidate mechanism for QPPs even when flare loops are fine-structured.